Planetary and Space Science 48 (2000) 1303–1320 www.elsevier.nl/locate/planspasci The study of the Martian atmosphere from top to bottom with SPICAM light on Mars Express Jean-Loup Bertaux a , D. Fonteyn b , O. Korablev c ; ∗ , E. Chasse ere d , E. Dimarellis a , J.P. Dubois a , A. Hauchecorne a , M. Cabane a , P. Rannou a , A.C. Levasseur-Regourd a , G. Cernogora a , E. Quemerais a , C. Hermans b , G. Kockarts b , C. Lippens b , M. De Maziere b , D. Moreau b , C. Muller b , B. Neefs b , P.C. Simon b , F. Forget d , F. Hourdin d , O. Talagrand d , V.I. Moroz c , A. Rodin c , B. Sandel e , A. Stern f a Service d’A eronomie du CNRS, 91371, Verri eres-le-Buisson, France b Belgian Institute for Space Aeronomy, 3 av. Circulaire, B-1180 Brussels, Belgium c Space Research Institute (IKI), 84=32 Profsoyuznaya, 117810 Moscow, Russia d Laboratoire de M et eorologie Dynamique, 4 place Jussieu, 75252 Paris Cedex 05, Paris, France e Lunar and Planetary Laboratory, 901 Gould Simpson Building, University of Arizona, Tucson, Arizona 85721, USA f South West Research Institute, Geophys., Astrophys., and Planet Sci., 1050 Walnut Ave., Suite 400, Boulder, CO 80302-5143, USA Received 2 June 1999; received in revised form 9 March 2000; accepted 28 March 2000 Abstract SPICAM Light is a small UV-IR instrument selected for Mars Express to recover most of the science that was lost with the demise of Mars 96, where the SPICAM set of sensors was dedicated to the study of the atmosphere of Mars (Spectroscopy for the investigation of the characteristics of the atmosphere of mars). The new conguration of SPICAM Light includes optical sensors and an electronics block. A UV spectrometer (118–320 nm, resolution 0.8 nm) is dedicated to Nadir viewing, limb viewing and vertical proling by stellar occultation (3.8 kg). It addresses key issues about ozone, its coupling with H2O, aerosols, atmospheric vertical temperature structure and ionospheric studies. An IR spectrometer (1.2–4:8 m, resolution 0.4 –1 nm) is dedicated to vertical proling during solar occultation of H2O, CO2, CO, aerosols and exploration of carbon compounds (3.5 kg). A nadir looking sensor for H2O abundances (1.0 –1:7 m, resolution 0.8 nm) is recently included in the package (0.8 kg). A simple data processing unit (DPU, 0.9 kg) provides the interface of these sensors with the spacecraft. In nadir orientation, SPICAM UV is essentially an ozone detector, measuring the strongest O3 absorption band at 250 nm in the spectrum of the solar light scattered back from the ground. In the stellar occultation mode the UV Sensor will measure the vertical proles of CO2, temperature, O3, clouds and aerosols. The density= temperature proles obtained with SPICAM Light will constrain and aid in the development of the meteorological and dynamical atmospheric models, from the surface to 160 km in the atmosphere. This is essential for future missions that will rely on aerocapture and aerobraking. UV observations of the upper atmosphere will allow study of the ionosphere through the emissions of CO, CO + , and CO + 2 , and its direct interaction with the solar wind. Also, it will allow a better understanding of escape mechanisms and estimates of their magnitude, crucial for insight into the long-term evolution of the atmosphere. The SPICAM Light IR sensor is inherited from the IR solar part of the SPICAM solar occultation instrument of Mars 96. Its main scientic objective is the global mapping of the vertical structure of H2O, CO2, CO, HDO, aerosols, atmospheric density, and temperature by the solar occultation. The wide spectral range of the IR spectrometer and its high spectral resolution allow an exploratory investigation addressing fundamental question of the possible presence of carbon compounds in the Martian atmosphere. Because of severe mass constraints this channel is still optional. An additional nadir near IR channel that employs a pioneering technology acousto-optical tuneable lter (AOTF) is dedicated to the measurement of water vapour column abundance in the IR simultaneously with ozone measured in the UV. It will be done at much lower telemetry budget compared to the other instrument of the mission, planetary fourier spectrometer (PFS). c  2000 Elsevier Science Ltd. All rights reserved. ∗ Corresponding author. E-mail address: oleg.korablev@aerov.jussieu.fr (O. Korablev). 0032-0633/00/$ - see front matter c  2000 Elsevier Science Ltd. All rights reserved. PII:S0032-0633(00)00111-2